Improvements in fuels

ABSTRACT

There is provided a method of providing an improved biofuel, by the presence of an additive which is the reaction product of (i) a compound containing the segment —NR 1 R 2  where R 1  represents a group containing from 4 to 44 carbon atom R 2  represents a hydrogen atom or a group R 1  (for example di-hydrogenated tallow amine) and (ii) a carboxylic acid having from 1 to 4 carboxylic acid groups or an acid anhydride or acid chloride thereof (for example phthalic acid or phthalic anhydride). The additives described combat problems arising from precipitation at temperatures above the cloud point.

The present invention relates to improvements in fuels derived wholly orin part from animal or vegetable oil sources. Such fuels are calledherein Bx fuels. Bx fuels may be derived entirely from animal orvegetable oil sources (B100 fuels) or they may comprise a proportion offuels derived from animal or vegetable oil sources, admixed with fuelsfrom other sources (for example mineral sources, or synthetic sources,e.g. Fischer-Tropsch sources). For example B20 herein is a fuel in which20 wt % of the fuel is from animal or vegetable oil sources and 80 wt %of the fuel is from other sources. The proportion may be lower still, asin the case of, for example, a B5 fuel.

A problem has become apparent in Bx fuels: blocking of filters indistribution systems and vehicles by precipitates in such fuels,typically at temperatures above the cloud point (CP) of the fuels. Theproblems have been seen in a wide range of Bx fuels, from B100 down toB5.

WO 2007/076163 describes such problems, and suggests that the problem offilter blocking arises as a result of the precipitation of crystals ofsteryl glycosides in fuels derived from biological sources. Sterylglycosides are found in plants and it is suggested that they are carriedover into Bx fuels.

WO 2007/076163 proposed a solution to the filter blocking problem;namely the removal of the steryl glycosides, for example using anadsorbent as an additive in conjunction with a process of filtration orcentrifugation, or both. In one example soy biodiesel was filteredthrough a bed of diatomaceous earth.

The proposals of WO 2007/076163 have the disadvantage that a separationstep is needed, in addition to the treatment of the Bx fuel with theadditive.

We are not bound by the explanation for the problem given in WO2007/076163. We believe it might be more complex, for example alsorelating to the total glycerides content, including monoglycerides,diglycerides and triglycerides, saturated or unsaturated. We arecertainly of the view that such problems now seen in Bx fuels areconnected with the Bx fuel component which is derived from vegetable oranimal sources, and are quite different from precipitation problemswhich have arisen in the past predominantly in mineral fuels. Thepresent invention seeks to solve this new problem notwithstanding thatan agreed scientific explanation of its nature or cause may follow.

By mineral fuels herein we mean fuels derived wholly from mineral (i.e.petroleum) sources. By mineral fuel component herein we mean themineral-derived component in a Bx fuel.

Filter blocking problems can occur at temperatures below the cloud pointin mineral and other fuels. Such problems have been closely analyzedover many years. Additives have been developed that allow fuels to beused at lower temperatures than would otherwise be possible.

The source of the problem of precipitation below the cloud point is thepresence of components such as so-called “waxes” (for example n-alkanesand methyl n-alkanoates that crystallise at low temperatures). This maycause the fuels to block filters and to become non-pourable.

Standardized tests have been devised to measure the temperature at whichthe fuel hazes (the cloud point—CP), the lowest temperature at which afuel can flow (the pour point—PP) and the cold filter pluggingpoint—CFPP); and the changes thereto caused by additives (ΔCP, ΔPP,ΔCFPP). The standardized tests for measuring PP and, especially, CP andCFPP are among the common working tools for persons skilled in the art.CP and CFPP may be further described as follows:

Cloud Point (CP)

The cloud point of a fuel is the temperature at which a cloud of waxcrystals first appears in a liquid when it is cooled under conditionsprescribed in the test method as defined in ASTM D 2500.

Until recently, it was considered that problems arising from theformation of precipitates would not occur at temperatures above thecloud point.

Cold Filter Plugging Point (CFPP)

At temperatures below the cloud point but above the pour point, the waxcrystals can reach a size and shape capable of plugging fuel lines,screens, and filters even though the fuel will physically flow. Theseproblems are well recognized in the art and have a number of recognizedtest methods such as the CFPP value (cold filter plugging point,determined in accordance with DIN EN 116).

Tests such as these were introduced to give an indication of lowtemperature operability as the cloud point test was considered to be toopessimistic.

The cold flow improvers (CFIs) and wax anti-settling additives (WASAs)which have been devised considerably ameliorate the problems ofprecipitation below the cloud point in fuels, and their effect canstudied by the test methods described above, comparing the resultsbetween unadditised fuels and additised fuels.

Some such additives may assist in keeping the so-called “waxes” insolution in the mineral fuel; others may alter their crystal morphologyor size, so that filterability and pourability are maintained in spiteof precipitation.

The additives devised to deal with the problems arising fromprecipitation below the cloud point have been very successful, to theextent that such fuels, suitably additised with, for example, CFIs (withor without WASAs), can be used even in severe low temperatureconditions. In many fuels the CFPP value may be lowered by 10-20° C.,compared with corresponding fuels without additives.

Additives are also known which improve the CFPP of Bx grades, includingB100 grade, and thus it would be expected that fuels treated in this wayshould have no operating problems even at temperatures significantlybelow the CP of the fuels.

However, as noted above, the problems which have emerged in Bx fuels arevery different from those which can arise in mineral fuels. Inparticular the precipitates cause filter blocking with Bx fuels attemperatures above the cloud point, whereas precipitation problems inmineral fuels occur below the cloud point, and generally at much lowertemperatures; and the chemical nature of the precipitates is believed tobe entirely different. As noted above the origin of the precipitation,though not fully understood, is believed to be entirelydifferent—specific compounds found in animal or vegetable sources, andnot found in mineral sources. The testing regimes described above areinappropriate for testing these precipitation issues in Bx fuels becausethey fail to predict adequately the temperature at which filters arelikely to block in real life situations such as in storage, distributionand use in vehicles and heating systems.

One of the reasons for this failure is believed to be that theprecipitation occurs during a period of “cold soaking” over severalhours or longer and therefore is not detected by tests such as CloudPoint or CFPP.

Critically, the precipitate does not redissolve when the temperature israised again. This is very different to conventional wax precipitationwhere at temperatures above the cloud point, wax can readily redissolve,particularly if kept dispersed in the fuel through use of WASAs.

Without wishing to be bound by theory, we believe that the precipitatescausing the problem of filter blocking at temperatures above the cloudpoint are present as minor constituents within the B100 and are moresoluble in the B100 than in mineral fuels and hence in Bx blends.Furthermore, it is thought that as the polarity of the mineral fuel isdecreased for example removal of sulphur, the solubility of theseconstituents will be even less and the problem will be exacerbated.

In the light of differences, in the nature of these precipitationphenomena below and above the cloud point, additives developed to solvea problem arising from precipitation below the cloud point,predominantly in mineral fuels, are not promising starting points tosolve a problem arising from precipitation in a Bx fuel, arising fromthe fuel component derived from an animal or vegetable oil. Indeed, itmust be borne in mind that Bx fuels have already contained additives ofthe type used to improve flow properties below the cloud point; and yetthe new problems of higher temperature filter blocking have stillarisen.

However, we have now found that, unexpectedly, there is one class ofadditive which is particularly effective at improving the flowproperties, and hence the filterability, of Bx fuels above the cloudpoint. This class was already known to improve the flow properties offuels below the cloud point. The finding of one class of additive which:

(a) improves the flow properties of fuels having an animal or vegetableorigin above the cloud point, and

(b) improves the flow properties of fuels, including mineral fuels,below the cloud point;

notwithstanding the different nature of the fuels and, in particular,the different nature of the respective problems and precipitates, isserendipitous.

In accordance with a first aspect of the present invention there isprovided a method of providing an improved Bx fuel, by the presence ofan additive which is the reaction product of (i) a compound containingthe segment —NR¹R² where R¹ represents a group containing from 4 to 44carbon atoms and R² represents a hydrogen atom or a group R¹, and (ii) acarboxylic acid having from 1 to 4 carboxylic acid groups or an acidanhydride or acid halide thereof.

Preferably R¹ is a hydrocarbyl group or a polyethoxylate orpolypropoxylate group.

Preferably the group R¹ is a hydrocarbyl group. Preferably the group R¹is predominantly a straight chain group.

The term “hydrocarbyl” as used herein denotes a group having a carbonatom directly attached to the remainder of the molecule and having apredominantly aliphatic hydrocarbon character. Suitable hydrocarbylbased groups may contain non-hydrocarbon moieties. For example they maycontain up to one non-hydrocarbyl group for every ten carbon atomsprovided this non-hydrocarbyl group does not significantly alter thepredominantly hydrocarbon character of the group. Those skilled in theart will be aware of such groups, which include for example hydroxyl,halo (especially chloro and fluoro), alkoxyl, alkyl mercapto, alkylsulfoxy, etc. Preferably the group R¹ is an organic group entirelypredominantly containing carbon and hydrogen atoms.

A hydrocarbyl group R¹is preferably predominantly saturated, that is, itcontain no more than one carbon-to-carbon unsaturated bond for every few(for example six to ten) carbon-to-carbon single bonds present. In thecase of a hydrocarbyl group R¹ having from 4 to 10 carbon atom it maycontain one unsaturated bond. In the case of a hydrocarbyl group R¹having from 11 up to 20 carbon atom it may contain up to two unsaturatedbonds. In the case of a hydrocarbyl group R¹ having from 21 up to 30carbon atom it may contain up to three unsaturated bonds. In the case ofa hydrocarbyl group R¹ having from 31 up to 40 carbon atom it maycontain up to four unsaturated bonds. In the case of a hydrocarbyl groupR¹ having from 41 up to 44 carbon atom it may contain up to fiveunsaturated bonds. Preferably, however, a hydrocarbyl group R¹ ispreferably a fully saturated alkyl group, preferably a fully saturatedn-alkyl group.

Preferably a group R¹ comprises from 6 to 36 carbon atoms, preferably 8to 32, preferably 10 to 24, preferably 12 to 22, most preferably 14 to20.

It will be appreciated that the group R¹ will typically include moietieswith a range of carbon atoms. The definitions C₄₋₄₄ . . . C₁₄₋₂₂ are notintended to denote that all R¹ groups must fall within the stated range.

The group R², when present, preferably conforms to the same definitionsas are given for R¹. R¹ and R² need not be the same. Preferably,however, R¹ and R² are the same.

Preferably the species (ii) is a carboxylic acid or an acid anhydridethereof.

However if an acid halide is used it is preferably an acid chloride.

Suitable compounds (i) include primary, secondary, tertiary andquaternary amines. Tertiary and quaternary amines only form amine salts.

Secondary amines, of formula HNR¹R², are an especially preferred classof compounds (i). Examples of especially preferred secondary aminesinclude di-octadecylamine, di-cocoamine, di-hydrogenated tallow amineand methylbehenyl amine. Amine mixtures are also suitable such as thosederived from natural materials. A preferred amine is a secondaryhydrogenated tallow amine, the alkyl groups of which are derived fromhydrogenated tallow fat composed of approximately 3-5% wt C₁₄, 30-32% wtC₁₆, and 58-60% wt C₁₈.

Quaternary amines, of formula [+NR¹R²R³R⁴ -An], are an especiallypreferred class of compounds (i). R¹ and R² are as defined above (but R²is not hydrogen). R³ and R⁴ independently represent a C(1-4) alkylgroup, preferably propyl, ethyl or, most preferably, methyl.+NR¹R²(CH₃)₂ represents a preferred cation. -An represents the anion.The anion may be any suitable species but is preferably a halide,especially a chloride. Where (i) comprises a quaternary amine, thereaction conditions may be adjusted to assist the reaction between (i)and (ii). Preferably the reaction conditions are adjusted by theintroduction of an auxiliary base. The auxiliary base is preferably aninorganic base, such as sodium methoxide, sodium ethoxide, or sodiumhydroxide. Preferably the inorganic base is a metal alkoxide or metalhydroxide. Alternatively, the quaternary amine salt may be preformed asthe corresponding basic salt, for example, a quaternary ammoniumhydroxide or alkoxide.

Also preferred are mixtures of primary and secondary amines, as species(i).

Also preferred are mixtures of secondary and quaternary amines, asspecies (ii).

Preferred carboxylic acids include carboxylic acids containing two,three or four carboxylic acid groups, and acid anhydrides and acidhalides thereof.

Examples of suitable carboxylic acids and their anhydrides includeaminoalkylenepolycarboxylic acids, for example nitrilotriacetic acid,propylene diamine tetraacetic acid, ethylenediamine tetraacetic acid,and carboxylic acids based on cyclic skeletons, e.g., pyromellitic acid,cyclohexane-1,2-dicarboxylic acid, cyclohexene-1,2-dicarboxylic acid,cyclopentane-1,2-dicarboxylic acid and naphthalene dicarboxylic acid,1,4-dicarboxylic acids, and dialkyl spirobislactones. Generally, theseacids have about 5 to 13 carbon atoms in the cyclic moiety. Preferredacids useful in the present invention are optionally substituted benzenedicarboxylic acids, e.g. phthalic acid, isophthalic acid, andterephthalic acid, and their acid anhydrides or acid chlorides. Optionalsubstituents include 1-5 substituents, preferably 1-3 substituents,independently selected from C(1-4)alkyl, C(1-4)alkoxy, halogen,C(1-4)haloalkyl, C(1-4)haloalkoxy, nitrile, —COON, —CO—OC(1-4)alkyl, and—CONR³R⁴ where R³ and R⁴ are independently selected from hydrogen andC(1-4)alkyl. Preferred halogen atoms are fluorine, chlorine and bromine.However unsubstituted benzene carboxylic acids are preferred. Phthalicacid and its acid anhydride are particularly preferred.

Preferably the molar ratio of compound (i) to acid, acid anhydride oracid halide (ii) is such that at least 50% of the acid groups(preferably at least 75%, preferably at least 90%, and most preferably100%) are reacted in the reaction between the compounds (i) and (ii),for example to form the amide and/or the amine salt.

Where compound (ii) comprises one or more free carboxylic acid groups,reaction conditions may be adjusted to allow reaction between compounds(i) and (ii), for example to form the respective amide or amine salt.The reaction conditions may be adjusted by raising reactiontemperatures. The reaction conditions may be adjusted by including adehydrating agent within the reaction mixture. The one or morecarboxylic acid groups may be activated in situ ready for coupling (i)and (ii), for example, by the use of such as carbodiimides (eg. EDCI).However, where activated forms of (ii) are employed, the activated formsof (ii) are preferably preformed, for example, as acid halides or acidanhydrides. Acid anhydrides are most preferred.

In the case of a preferred reaction, between a compound (i) and adicarboxylic acid, or acid anhydride or acid halide thereof, preferablythe molar ratio of compound (i) (or mixtures of compounds (i), in thatsituation) to acid, acid anhydride or acid halide (ii) (or mixedcompounds (ii), in that situation) is at least 0.7:1, preferably 1:1,preferably at least 1.5:1. Preferably it is up to 3:1, preferably up to2.5:1. Most preferably it is in the range 1.8:1 to 2.2:1. A molar ratioof 2:1, (i) to (ii) is especially preferred. Also preferred is a molarratio of 1:1.

It will be understood by those skilled in the art that compound (ii) isdefined as the original starting material. However, preferred productsmay be obtained by step-wise reactions involving reacting compound (i)with an adduct of compound (ii), particularly where (ii) has alreadyreacted in with a compound (i) to form an intermediate. Such anintermediate may be fully isolated or partially isolated so as to allowstep-wise reactions. Such an intermediate may comprise amono-amide/mono-carboxylic acid adduct, for instance, where in a firststep a first equivalent of (i) is reacted with a dicarboxylic acid, acidanhydride, or acid halide. Partial isolation may therefore be mereisolation of the reaction mixture resulting from the first step of areaction to form the mono-amide/mono-carboxylic acid. In suchcircumstances, a subsequent reaction of compound (i) (optionally adifferent compound (i) than that used in the first step) with themono-amide/mono-carboxylic acid adduct may yield further derivatives,for instance, a diamide or a mono-amide/ammonium carboxylate salt. Sucha step-wise process provides for greater selectivity of either or bothof an amide group and/or an ammonium salt, especially where the aminesof said amide group and said ammonium group are different, such as when(i) essentially comprises more than one amine.

In the case of a preferred reaction, between a secondary amine as theonly compound (i) and a dicarboxylic acid, or acid anhydride or acidhalide thereof, preferably the molar ratio of amine (i) to acid, acidanhydride or acid halide (ii) is at least 1:1, preferably at least1.5:1. Most preferably it is in the range 1.8:1 to 2.2:1. A molar ratioof 2:1, (i) to (ii) is especially preferred.

In the case of another preferred reaction, between a quaternary ammoniumsalt as the only compound (i) and a dicarboxylic acid, or acid anhydrideor acid halide thereof, preferably the molar ratio of quaternaryammonium salt (i) to acid, acid anhydride or acid halide (ii) is atleast 1:1, preferably at least 1.5:1. Most preferably it is in the range1.8:1 to 2.2:1. A molar ratio of 2:1, (i) to (ii) is especiallypreferred.

Preferred reaction products for use in this invention contain at leastthe mono-amide adduct and quaternary ammonium salt and this may beachieved by using a mixture of compounds as compound (i), preferablyboth a secondary amine and a quaternary ammonium compound.

Another preferred reaction employs both a secondary amine and aquaternary ammonium salt as compounds (i). Preferably the ratio of thesecondary amine to the quaternary ammonium salt in the reaction mixtureis 30-70% to 70-30% molar/molar, preferably 40-60% to 60-40%, and mostpreferably they are present in equimolar amounts. Consistent with whatis stated above, therefore, this reaction employs in its most preferredembodiment equimolar amounts of the secondary amine, the quaternaryammonium salt and the acid, acid anhydride or acid halide (ii).

Preferably the reaction between the compound (i) and the carboxylicacid, acid anhydride or acid halide forms one or more amide, imide orammonium salts, combinations of these within the same compound, andmixtures of these compounds.

Thus, in one preferred embodiment a dicarboxylic acid, acid anhydride oracid halide is reacted with a secondary amine in a mole ratio of 1:2such that one mole of the amines form an amide and one mole forms anammonium salt.

An especially preferred additive is a N,N-dialkylammonium salt of2-N′,N′-dialkylamide benzoic acid, which suitably is the reactionproduct of di(hydrogenated) tallow amine (i) and phthalic acid or itsacid anhydride (ii); preferably at a molar ratio of 2:1.

An especially preferred additive is the reaction product ofdi(hydrogenated) tallow amine (i) and phthalic acid or its acidanhydride (ii); preferably at a molar ratio of 1:1.

Other preferred additives are the reaction products (hydrogenated)tallow amine with EDTA reaction in a molar ratio of 4:1 with removal offour moles of water or two moles of water to form respectively thetetraamide derivative or the diamide diammonium salt derivative.

Another preferred additive is the reaction product of one mole ofalkylspirobislactone, for example dodecenyl-spirobislactone with onemole of mono-tallow amine and one mole of di-tallow amine.

The fuel composition of the present invention may contain at least 1 wt% of fuel derived from animal or vegetable sources, for example at least2 wt %, at least 3 wt %, at least 4 wt %, at least 5 wt %, at least 6 wt%, at least 8 wt %, or at least 10 wt %, of fuel derived from animal orvegetable sources. Some embodiments may contain at least 15 wt %, or atleast 20 wt %, of fuel derived from animal or vegetable sources. Thefuel composition may contain up to 99 wt % of fuel derived from animalor vegetable sources, for example up to 95 wt %, up to 90 wt %, up to 85wt %, up to 80 wt %, up to 75 wt %, up to 70 wt %, up to 60 wt %, up to50 wt %, up to 40 wt %, up to 30 wt %, up to 25 wt %, up to 20 wt %, upto 15 wt %, or up to 12 wt %, of fuel derived from animal or vegetablesources.

A fuel which comprises 100% fuel produced from an animal or vegetablesource is denoted as B100, a fuel which comprises 90% mineral diesel and10% biodiesel is known as B10; fuel comprising 50% mineral diesel and50% biodiesel is known as B50; and so on.

Fuel of animal or vegetable origin may include ethyl or methyl esters offatty acids of biological origin. Starting materials for the productionof such fuel include, but are not limited to, materials containing fattyacids. These materials include, without limitation, triacylglycerols,diacylglycerols, monoacylglycerols, phospholipids, esters, free fattyacids, or any combinations thereof. The diesel is produced by incubatingthe material including the fatty acids with a short chain alcohol in thepresence of heat, pressure, a catalyst, or combinations of any thereofto produce fatty acid esters of the short chain alcohols.

The fatty acids used to produce the fuel may originate from a widevariety of natural sources including, but not limited to, vegetable oil,canola oil, safflower oil, sunflower oil, nasturtium seed oil, mustardseed oil, olive oil, sesame oil, soybean oil, com oil, peanut oil,cottonseed oil, rice bran oil, babassu nut oil, castor oil, palm oil,palm oil, rapeseed oil, low erucic acid rapeseed oil, palm kernel oil,lupin oil, jatropha oil, coconut oil, flaxseed oil, evening primroseoil, jojoba oil, camelina oil, tallow, beef tallow, butter, chicken fat,lard, dairy butterfat, shea butter, used frying oil, oil miscella, usedcooking oil, yellow trap grease, hydrogenated oils, derivatives of theoils, fractions of the oils, conjugated derivatives of the oils, andmixtures of any thereof.

Preferably the precipitates which form above the cloud point and whichthe present invention seeks to combat are not revealed by cloud pointtest ASTM D 2500.

Preferably the precipitates which form above the cloud point and whichthe present invention seeks to combat are not revealed immediatelymerely by cooling the fuel to a given temperature. Preferably they formfollowing an incubation period, by holding the fuel at a temperatureabove the cloud point for a incubation period. Preferably the incubationperiod is at least 4 hours, preferably at least 12 hours, preferably atleast 16 hours, preferably at least 48 hours, preferably at least 96hours.

Preferably the precipitates which form above the cloud point and whichthe present invention seeks to combat are not removed merely by raisingthe temperature of the fuel above the temperature at which they formed.

Preferably the Bx fuel is a middle distillate fuel, generally boilingwithin the range of from 110 to 500, e.g. 150 to 400° C. Preferably itis a Bx fuel for use in diesel engines or heating fuel oil.

In one embodiment the fuel is B100. Preferably however the fuel is ablend of fuel derived from animal or vegetable sources and fuel derivedfrom mineral sources and/or synthetic sources (e.g. FT fuels, derivedfrom the Fischer-Tropsch process).

Preferably the fuel is a blend of a fuel derived from vegetable sourcesand a fuel derived from non-vegetable sources; preferably from mineralsources.

The Bx fuel may contain other flow-improving additives to provide theusual benefits, in reducing the CP and CFPP. Such compounds may includeCFIs and WASAs.

Examples of such additives and their use in petroleum-based oils aredescribed in U.S. Pat. No. 3,048,479; GB 1263152; U.S. Pat. No.3,961,916; U.S. Pat. No. 4,211,534; EP 153176A; and EP 153177A.

U.S. Pat. No. 3,048,479 describes ethylene-vinyl ester pour depressantsfor middle distillates. GB 1263152 describes distillate petroleum oilcompositions containing ethylene ester copolymers. The preferredcopolymers are of ethylene and vinyl acetate. U.S. Pat. No. 3,961,916describes middle distillate compositions with improved filterabilitycontaining mixtures of two different EVA copolymers. U.S. Pat. No.4,211,534 describes combinations of ethylene polymer, polymer havingalkyl side chains, and nitrogen containing compound to improve cold flowproperties of distillate fuel oils. EP 153176A and EP 153177A describepolymers or copolymers containing an n-alkyl ester of amono-ethylenically unsaturated C4 to C8 mono- or dicarboxylic acid.

Use of an ethylene vinyl acetate copolymer as a CFI in conjunction withan adduct of compounds (i) and (ii) as defined herein, is especiallypreferred.

Preferably the Bx fuel is a low sulphur content fuel, preferably havinga sulphur content less than 200 ppm, preferably less than 100 ppm,preferably less than 50 ppm, preferably less than 20 ppm, preferablyless than 15 ppm, preferably less than 10 ppm.

Preferably the additive is present in the fuel in an amount (as activematerial) of from 5 mg/kg fuel, preferably from 10 mg/kg fuel,preferably from 20 mg/kg fuel, preferably from 30 mg/kg fuel.

Preferably the additive is present in the fuel in an amount (as activematerial) up to 500 mg/kg, preferably up to 200 mg/kg fuel, preferablyup to 100 mg/kg fuel, preferably up to 80 mg/kg fuel, preferably up to60 mg/kg fuel, preferably up to 45 mg/kg fuel.

The additive may be added to Bx fuel which is known to exhibit afiltration problem above the cloud point, to reduce the problem or,preferably, to obviate the problem by preventing precipitation above thecloud point.

Reducing or solving the problem may be achieved by reducing the size orquantity of the precipitates which may appear in the Bx fuel above thecloud point, or by controlling the morphology of the precipitates in theBx fuel above the cloud point.

Preferably, however, the additive is added to Bx fuel in order toprevent the emergence of precipitates above the cloud point. Bypreventing the emergence of precipitates above the cloud point we meanthat detectable precipitates do not appear in the Bx fuel under normalstorage or use conditions.

In accordance with a second aspect of the present invention there isprovided the use of an additive which is the reaction product of (i) acompound containing the segment —NR¹R² where R¹ represents a groupcontaining from 4 to 44 carbon atoms and R² represents a hydrogen atomor a group R¹, and (ii) a carboxylic acid having from 1 to 4 carboxylicacid groups or an acid anhydride or acid halide thereof, in order tomaintain the filterability of the Bx fuel above the cloud point of theBx fuel.

In accordance with a third aspect of the present invention there isprovided the use of an additive which is the reaction product of (i) acompound containing the segment —NR¹R² where R¹ represents a groupcontaining from 4 to 44 carbon atoms and R² represents a hydrogen atomor a group R¹, and (ii) a carboxylic acid having from 1 to 4 carboxylicacid groups or an acid anhydride or acid halide thereof in order toprevent the emergence of precipitates in the Bx fuel above the cloudpoint of the Bx fuel.

Aspects and preferred features described above following presentation ofthe first aspect apply also to the second aspect and third aspect,including: ways in which filterability may be maintained; ways in whichprecipitation may be controlled, inhibited or prevented; preferredcompounds (i) and (ii); preferred ratios of (I) to (II); preferred Bxfuels; and preferred concentrations of the additive in the Bx fuel.

In accordance with a fourth aspect of the present invention there isprovided a Bx fuel having improved flow properties above the cloud pointof the Bx fuel, the fuel comprising an additive which is the reactionproduct of (i) a compound containing the segment —NR¹R² where R¹represents a group containing from 4 to 44 carbon atoms and R²represents a hydrogen atom or a group R¹, and (ii) carboxylic acidhaving from 1 to 4 carboxylic acid groups or an acid anhydride or acidhalide thereof.

In accordance with a fifth aspect of the present invention there isprovided an additive composition comprising an additive which is thereaction product of (i) a compound containing the segment —NR¹R² whereR¹ represents a group containing from 4 to 44 carbon atoms and R²represents a hydrogen atom or a group R¹, and (ii) a carboxylic acidhaving from 1 to 4 carboxylic acid groups or an acid anhydride thereofin a solvent.

In accordance with a sixth aspect of the present invention there isprovided a method of improving the filter blocking tendency of a Bx fuelby addition of an additive as defined in any preceding claim.

The invention will now be further described, by way of example, withreference to the following test descriptions.

EXAMPLE SET A

The tests involved using a modified version of the IP387 (Determinationof filter blocking tendency of gas oils and distillate diesel fuels)method.

In the IP 387 method, a sample of the fuel to be tested is passed at aconstant rate of flow through a glass fibre filter medium. The pressuredrop across the filter is monitored, and the volume of fuel passing thefilter medium within a prescribed pressure drop is measured.

The filter blocking tendency (FBT) can be described in one of thefollowing ways:

-   -   The pressure drop (P) across a GF/A (glass fibre) filter medium        for 300 ml of fuel to pass at a rate of 20 ml/min is recorded.    -   The volume of fuel (v) passed when a pressure of 105 kPa is        reached. This method of report is used when less than 300 ml        passes at that pressure drop.

The FBT may be expressed on a single scale by combining these using thefollowing formulae

${FBT} = {{\sqrt{1 + \left( \frac{P}{105} \right)^{2}}\mspace{14mu} {and}\mspace{14mu} {FBT}} = \sqrt{1 + \left( \frac{300}{V} \right)^{2}}}$

Thus when exactly 300 ml passes through the filter at a pressure of 105kPa, the FBT is 1.41. Values of FBT >1.41 indicate that less than 300 mlpass through the filter before a pressure of 105 kPa is reached. Valuesof FBT <1.41 indicate that 300 ml pass through the filter at a pressureof less than 105 kPa

An FBT <1.4 is considered to be a good result.

The modification to the IP 387 method relates to thermal conditioningand cold soak of a sample being tested.

-   -   1. the sample is heated to a temperature of 60° C. for 3 hours        and then allowed to cool to 20° C.    -   2. The sample is then cooled to 5° C. for 16 hours and then        allowed to warm to room temperature.

Following this conditioning, the Filter Blocking Tendency is determinedusing IP 387.

The base fuel used in these tests was a B5 fuel which met therequirements of DIN EN 590 and contained a commercially available coldflow additive believed to comprise EVA copolymers in an amount effectiveto achieve a CFPP of <−15° C. The fuel had the following properties:

Method Method Number Result Density at IP 365 0.8417 g/ml 15° C. CFPP IP309   −17° C. Cloud Point ASTM D5772  −5.8° C. Distillation IP 123 IBP175.5° C.  5% 195.9° C. 10% 206.4° C. 20% 226.0° C. 30% 244.0° C. 40%260.5° C. 50% 275.0° C. 60% 288.7° C. 70% 302.3° C. 80% 317.2° C. 90%335.3° C. 95% 348.6° C. FBP 359.5° C.

Testing was carried out using

a) this base fuel,

b) this base fuel additised with 37.5 mg/kg of Compound A, and

c) this base fuel additised with a commercial WASA (believed to be anitrogen-containing polymeric WASA) long used with success to improvethe flow properties of mineral diesel fuels below the cloud point.

To prepare Compound A phthalic anhydride (7.4 g) was mixed with di(hydrogenated tallow) amine (Commercially available as Armeen 2HT)(50.02 g) at a molar ration of 1:2 in Shellsol AB solvent (57.5 g). Thereaction mixture was heated at 65° C. for approximately 6 hours.

The results are as follows:

(b) base fuel + (c) base fuel + 37.5 mg/kg 150 mg/kg Sample (a) basefuel Compound A WASA Filter Blocking 1.8 1.23 1.87 Tendency Initialpressure 10 10 10 (kPa) Final pressure 105 75 105 (kPa) Volume filtered200 300 190 (ml) Test temperature 23 23 23 (° C.)

Using Compound A allowed all 300 ml of the fuel to pass through thefilter without the pressure reaching 105 kPa. The improvement over theperformance of the base fuel is very marked. In contrast it is observedthat the commercial WASA, at a higher treat rate, causes no discernableimprovement in the flow properties of the base fuel.

EXAMPLE SET B

In Example Set B the testing was the same as in Example Set A but thebase fuel (“Basefuel 2”) also met the requirements of DIN EN90 and was aB10 fuel prepared from a standard diesel meeting the specifications ofCEC Fuel Specification RF-06-03, blended with rapeseed methyl ester(RME) and a commercially available cold flow additive believed tocomprise EVA copolymers in an amount effective to achieve a CFPP of<−15° C.

The FBT of Basefuel 2 was 2.52.

The FBT of Basefuel 2 additised with 37.5 mg/kg of Compound A was 1.03.

The FBT of Basefuel 2 additised with 150 mg/kg of WASA (believed to be anitrogen-containing polymeric WASA) was 2.03.

1. A method of treating a Bx fuel in order to improve the filterabilityof the Bx fuel above the cloud point of the Bx fuel, comprising addingto a Bx fuel a reaction product of (i) a compound containing the segment—NR¹R² where R¹ represents a group containing from 4 to 44 carbon atomsand R² represents a hydrogen atom or a group R¹, and (ii) a carboxylicacid having from 1 to 4 carboxylic acid groups or an acid anhydride oracid halide thereof; wherein the Bx fuel comprises fuel derived fromanimal or vegetable oil sources admixed with fuel derived from mineralor synthetic sources; wherein the Bx fuel has a sulphur content lessthan 200 ppm; wherein the Bx fuel contains at least 4 wt % of fuelderived from animal or vegetable sources; and wherein the additive ispresent in the Bx fuel in an amount (as active material) of from 10mg/kg up to 200 mg/kg.
 2. The method as claimed in claim 1, wherein thegroup R¹ is a predominantly straight chain, substantially saturatedgroup comprising from 10 to 24 carbon atoms.
 3. The method as claimed inclaim 1, wherein the group R² is a group R¹.
 4. The method as claimed inclaim 3, wherein the compound (i) is a secondary amine of formula HNR¹R²where R¹ and R² are as defined in claim 3; or is an ammonium salt havingthe cation +NR¹R²R³R⁴ where R¹ and R² are as defined in claim 3 and R³and R⁴ independently represent a C(1-4) alkyl group.
 5. The method asclaimed in claim 1, wherein the carboxylic acid is anaminoalkylenepolycarboxylic acid selected from the group consisting ofnitrilotriacetic acid, propylene diamine tetraacetic acid,ethylenediamine tetraacetic acid, dialkyl spirobislactones, andcarboxylic acids based on cyclic skeletons having 5 to 13 carbon atomsin the cyclic moiety, wherein the carboxylic acids based on cyclicskeletons are selected from the group consisting of pyromellitic acid,cyclohexane-1,2-dicarboxylic acid, cyclohexene-1,2-dicarboxylic acid,cyclopentane-1,2-dicarboxylic acid, naphthalene dicarboxylic acid,1,4-dicarboxylic acids and benzene dicarboxylic acids.
 6. The method asclaimed in claim 5, wherein the carboxylic acid is an acid anhydride oran acide halide.
 7. The method as claimed in claim 1, wherein the molarratio of compound (i) to acid anhydride or acid halide (ii) is such thatat least 50% of the acid groups are reacted in the reaction between thecompounds (i) and (ii).
 8. The method as claimed in claim 1, whereincompound (i) is a secondary amine and/or quaternary ammonium salt andcompound (ii) is a dicarboxylic acid, or an acid anhydride or acidhalide thereof, wherein the molar ratio of compound(s) (i) to acid, acidanhydride or acid halide (ii) is at least 1:1.
 9. The method as claimedin claim 1, wherein said additive is present in the Bx fuel in an amountof from 20 mg/kg fuel up to 80 mg/kg fuel.
 10. The method as claimed inclaim 1, wherein the Bx fuel is a blended fuel comprising a fuelcomponent derived from an animal or a vegetable oil source and a fuelcomponent derived from a mineral source.
 11. The method as claimed inclaim 10, wherein the Bx fuel further comprises one or more compoundswhich improve the flow properties of the fuel derived from the mineralsource at a temperature below the cloud point of the Bx fuel. 12-14.(canceled)
 15. A Bx fuel comprising a fuel additive which is thereaction product of (i) a compound containing the segment —NR¹R² whereR¹ represents a group containing from 4 to 44 carbon atoms and R²represents a hydrogen atom or a group R¹, and (ii) an optionallysubstituted benzene dicarboxylic acid or an acid anhydride or acidhalide thereof, wherein the Bx fuel has a sulphur content less than 200ppm and contains at least 4 wt % of fuel derived from animal orvegetable sources; and wherein the additive is present in the Bx fuel inan amount as active material of from 10 mg/kg up to 200 mg/kg so as toprovide improved filterability of the Bx fuel above the cloud point ofthe Bx fuel.
 16. (canceled)
 17. The method as claimed in claim 5,wherein the benzene dicarboxylic acid is selected from the groupconsisting of isophthalic acid, terephthalic acid and phthalic acid. 18.The method as claimed in claim 7, wherein the benzene dicarboxylic acidis an acid anhydride or an acid halide.